In the course of provisioning, qualifying, installing and repairing copper loops that make up today's telecommunications infrastructures, installation and repair technicians and other service provider personnel are required to perform a variety of tests, checks, and analyses on each copper loop. In many cases, these activities must be carried out repeatedly before services to a customer can be provided or reestablished. For reliability, it desired that service personnel be able to run the same suite of tests every time, in the same way, with the same criteria for pass and fail. Although there are currently a prescribed series of manual steps to be carried out, sometimes they are followed but sometimes they are not, which obviously leads to inconsistent results.
In order to accomplish these tasks, service personnel are often provided with extensive training that is intended to address not only the use of diagnostic equipment, but also appropriate methods and procedures to be applied to any number of specific circumstances. The vast majority of these test, checks and analyses are currently performed by a service technician whose is equipped with test equipment at one end, or one location of the loop under test. These methods, while useful for some testing, have inherent shortcomings that can affect the overall quality of the copper loop and, consequently, the services being delivered to the end customer. These methods are, in effect, ‘open loop’ solutions that fail to adequately provide metrics for total loop signal loss, undue power influence, circuit noise, circuit balance, overall resistive and capacitive characteristics and an accurate assessment of overall loop length. Moreover, following extensive training, mobile service personnel must each be equipped with costly diagnostic service equipment, in lieu of a system where diagnosis and management originate from a central location.
In a typical situation, the service technician will access the loop at a box on the side of the customer's premises, which is generally referred to as a Network Interface Device or NID, that allows the technician to isolate inside wiring and all the customer's phones from the regular phone line, because that is the point to which they are responsible. The technician will advise the customer to stay off their phone line and, when accessing the NID, the technician will also disconnect the customer premises inside and start testing from that point backwards, now knowing that the customer's equipment is not influencing the test measurements.
At this location the technician typically uses a hand-held meter to individually measure AC voltage, DC voltage and loop current. During each measurement, the technician has to select the dial position setting, make the reading and then physically generate a hard copy record of the reading. Although the technician is required to turn in the hard copy upon which the measurement readings were tabulated this does not always happen. If the measured loop current is above a prescribed value considered by the technician to be high enough (e.g. on the order of twenty milliamps) to proceed with further testing, he will set the test meter to a mode where it is static, and he can then use his butt set to bridge on the line, dial into central office test equipment, such as a SASS unit, or dial into a milliwatt 1004 Hz reference tone device, by inputting a DTMF key sequence to make that device send a 1004 Hz tone back at him. Once he hears a tone he switches his meter mode to ‘measure loss’, in an effort to measure the total loop loss of the line. Again, the technician reads the meter and he records the reading on a piece of paper.
If the results of the measurements are satisfactory, the technician will reassemble the connections and then run a further test to determine whether the problem is inside the customer premises or not, giving the customer the option to proceed at a given service charge. Most of the time the problem is not in the customer premises. Instead, the problem typically lies in the last major section of the copper cable plant which predominately, though not always, has been subdivided into two major sections, customarily referred to as facilities-one (F1) and facilities-two (F2). The F1 cable plant section corresponds to the bulky legacy wires coming out of the central office that have been wired for years. Sometimes this section of the cable has problems, but not often. On the other hand it has been found that the about eighty-five percent of the problems occur in the F2 section, since it is this section of the cable plant that is most often accessed and manipulated by service technicians. A not uncommon scenario is to effect a repair of one line in the F2 section, while simultaneously and inadvertently creating a fault (e.g., break) in another line in that section.
Although the technician will typically spend most of his time at the side of the customer premises, sometimes he will access the circuit under test at a relatively ‘upstream’ location, which may be a mile or two away at a crossbox distribution point, which is a farther back into the network. If a measurement taken at this location is exceedingly high or above a threshold, most of the time the technician can fix it. However, sometimes, there is nothing the servicing personnel can do about it, due to excessive power influence in an area, for example there may be a thousand copper pairs going into one neighborhood that are not properly grounded. In this case, the technician will often back up one step and test five or six lines in an attempt to get a reasonable idea of what it is suppose to look like.
The hand-held meters currently employed either manually step through these operations or guide the user to manually step through them, in order to measure the loss. The user will call into a designated test location, which generates a milliwatt signal, a 1004 Hz reference signal, and measure that loss. The service technician then hangs up and goes back on hook with his butt set, placing the meter in quiescent mode, and dials into another device called a quiet termination device, which places a 600 or a 900 ohm termination across the line. The technician then places the meter in a mode called ‘power influence’ mode and measures the power influence on the line. The power influence is effectively longitudinal noise (to ground), which is converted from the tip and ring signal to the tip and ring ground signal. In addition, a measurement is made of metallic noise, which is the tip and ring conductor without the ground component. Both of those manual tests are performed via the meter at different times, and the technician is required to take the readings and record the readings on paper.
After this series of tests has been completed, the technician is supposed to manually subtract the noise measurement from the power influence measurement to provide a third reading called longitudinal balance. Once this has been done, the technician does not usually proceed any further. Unfortunately it has been found that in some instances technicians have failed to perform the power influence test and the longitudinal noise test, due to their lack of training as to how to make these measurements, what they mean and what to do about them. Although the steps of each of the testing procedures are documented, it turns out that for one reason or another they are not being performed—either due to lack of training lack of equipment or lack of experience to know what to do about a reading. Indeed, it is not uncommon to have a technician take a reading, and then make a guess as to whether it is within the ‘ballpark’ of a threshold, in order to assign a pass or fail status to the test. Presently the above process takes about eight minutes and is somewhat error prone because the technician is required to record the meter reading. Even when he does, as an example, the technician may look at the meter needle, see that it is it somewhere between 20 and 30, maybe a value of about 25 would be ok, and he writes that down.
The second part of the line test is something the technician can, but often doesn't perform. That is, he can call into an automated test system, or call a person who has access to an automated test system. The system is typically referred to as a mechanized loop tester or MLT, or it may be a direct access test unit or DATU. The loop tester accesses the telephone that one would like to test by either directly inputting the line number, or by capturing the phone number from the line the technician is calling from in the case of the DATU. This unit takes the telephone number that you want to test and tells the Central Office switching system to remove the line circuit electrically through a relay switch in the line card, so that the dial tone will go away from this line, allowing the line to be tested without the influence of 48 volts battery and any dial tone that might be provided in order to serve the customer, effectively making the line a dry line.
Although this part of the line test takes only about two minutes, queuing into the test system can take ten or fifteen minutes. It is one is one of the reasons that a speaker is provided on a butt set, as telephone technicians will call in and then proceed to wait in queue, so they turn their speaker on and hook the butt set out at the side of the road, and then clean their truck or do other things while they are waiting to get into the queue for testing. Even if they are the only one in queue, it typically can take two to three minute test time.
From an MLT perspective, the DATU will take the battery off of the line and perform some basic voltage resistance, capacitance readings to tell approximately what the length of the line is based on capacitance, how much DC voltage there is, how much AC voltage there is, if any, and a resistance reading to determine if there is any resistive leakage on the line. This constitutes the central office part of the test system. As pointed out above, it usually requires a couple of minutes, or slightly longer if it is an extended line, like a digital loop carrier line where there is some additional signaling that has to happen.
Most telephone lines served out of the central office contain regular copper lines from the point they leave the central office to the point they get to the customer premises. Sometimes they are not. Sometimes they are lines called digital loop carrier (DLC) lines, which correspond to digital service transported over a T1 carrier link and then demultiplexed at the other end in the neighborhood before it arrives at the customer premises. Those tests take on the order of another 35–45 seconds to perform.
Unfortunately, there is currently no correlation between the first suite of manual tests that involve the technician dialing in with his butt set, doing a loss measurement, doing a noise measurement, and doing a power influence measurement, and the second suite of tests that involve dialing into again to the maintenance center and asking someone to preform a test. As a result, the second suite of tests may not be performed at all. The only tests performed are those of the first suite. The technician looks at it and he has five or six test results with which to decide if the line is going to be ok or not, or how to troubleshoot.
The second part of the test is like reading the manual; from a practical standpoint it is only performed when the technician has no answer and realizes he must call in and get someone else to remotely run another test on the line. At this point, the technician is dependent upon a person called a screener, who performs the test and sees the results displayed on a screen in front of him, so that he can tell the technician what it says. In some of the newer systems, the technicians can actually take a hand-held terminal and dial in on a modem line, if they can find one, and do that test for themselves and see the results on the screen. This usually takes about five minutes.
If one considers all of the above procedures, it can be seen that the technician has a half a dozen independent steps to perform and several phone calls to make via a very labor intensive process. Once all these tests have been completed, the technician is in possession of a substantial amount of information, but no one else has that information. There is no record of it anywhere unless the technician manually writes it down and attaches a paper copy to the trouble ticket when he turns it in. That is how test systems typically work today. Moreover, as noted above, many of the technicians do not really understand the results they see on their screen and what to do about them. The test usually requires between eight to twelve minutes of time, and it is a single-ended test. In other words, only the technician in the field has the test results. Nobody else knows what he has done or what the results that testing are.